DUV scanner linewidth control by mask error factor compensation

ABSTRACT

Linewidth variations and bias that result from MEF changes and reticle linewidth variations in a printed. substrate are controlled by correcting exposure dose and partial coherence at different spatial locations. In a photolithographic device for projecting an image of a reticle onto a photosensitive substrate, an adjustable slit is used in combination with a partial coherence adjuster to vary at different spatial locations the exposure dose received by the photosensitive substrate and partial coherence of the system. The linewidth variance and horizontal and vertical or orientation bias are calculated or measured at different spatial locations with reference to a reticle, and a corrected exposure dose and partial coherence is determined at the required spatial locations to compensate for the variance in linewidth and bias on the printed substrate. Improved printing of an image is obtained, resulting in the manufacturer of smaller feature size semiconductor devices and higher yields.

FIELD OF THE INVENTION

The present invention relates generally to photolithography, andparticularly to an exposure system to control variations in linewidth inan image that is printed and used in the manufacture of semiconductordevices.

BACKGROUND OF THE INVENTION

In semiconductor manufacturing, the image of a reticle or mask isprojected onto a photosensitive substrate or wafer. As semiconductordevices become ever smaller, the feature size of the images printed onthe semiconductor device also become smaller. Correctly imaging andprinting these small feature sizes onto a photosensitive substratebecomes increasingly difficult as the feature size is reduced. As thefeature sizes approach the fraction of exposure wavelength, correctimaging is often difficult to obtain. There are many variables thatdetermine the image quality and correct printing of a pattern on areticle. The lines on a reticle to be reproduced may vary as a functionof the feature size, type, and location in the field. The image may alsovary as a function of the orientation or direction of the feature on themask or reticle being imaged. There have been many attempts to improvethe imaging characteristics of a photolithographic device to improveimage quality and provide consistent printing. One suchphotolithographic system is disclosed in U.S. Pat. No. 5,383,000entitled “Partial Coherence Varier For Microlithographic Systems”issuing to Michaloski et al on Jan. 17, 1995, which is hereinincorporated by reference. Therein disclosed is a microlithographicsystem utilizing an adjustable profiler that is actually movable alongthe optical axis in the illumination path for imposing a predeterminedangular profile of the illumination. Another device for improvingimaging in a photolithographic system is disclosed in U.S. Pat. No.6,013,401 entitled “Method of Controlling Illumination Field To ReduceLinewidth Variation” issuing to McCullough et al on Jan. 11, 2000, whichis herein incorporated by reference. Therein disclosed is an dynamicallyadjustable slit for controlling the exposure dose at different spatiallocations during a scanning exposure of a reticle. The adjustments inexposure are made in a direction perpendicular to the direction of scanof the illumination field. Another photolithographic system is disclosedin U.S. patent application Ser. No. 09/232,756 entitled “Dose ControlFor Correcting Linewidth Variation In The Scan Direction” filed Jan. 15,1999, by McCullough, which is herein incorporated by reference. Thereindisclosed is a device for varying the exposure dose as a function ofdistance in a scan direction for reducing linewidth variation. Whilethese photolithographic systems and exposure devices and methods haveimproved image quality and the printing of features upon aphotosensitive substrate, there is a need for yet further improvement,especially as the feature size is reduced and the need for better imagequality and correct reproduction of the image. on a photosensitivesubstrate.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus forcorrecting for printed feature size variations over a field byselectively adjusting the dose and partial coherence in a scanningphotolithographic device. A scanning photolithographic device or toolcomprises an illumination source forming an illumination field that isscanned, projecting the image of a mask or reticle onto a photosensitivesubstrate. The illumination field is adjusted to vary the exposure doseat predetermined spatial locations and an adjustable array opticalelement selectively varies at different spatial locations the numericalaperture of the illumination, thereby varying the partial coherence ofthe system.

Accordingly, it is an object of the present invention to improve theprinting of features on a photosensitive substrate.

It is a further object of the present invention to correct for featuresize variations resulting from the mask error factor.

It is yet a further object of the present invention to correct forreticle linewidth variations.

It is an advantage of the present invention that it is easily modifiableto accommodate different features to be printed.

It is a further advantage of the present invention that it reduceslinewidth variances in printed features.

It is yet a further advantage of the present invention that it reduceshorizontal and vertical bias in printed features.

It is a feature of the present invention that an adjustable slit is usedto vary the exposure dose.

It is another feature of the present invention that an array opticalelement is used to vary the illumination numerical aperture andresulting partial coherence at different locations in the illuminationfield to minimize reticle feature variation induced horizontal/verticalbias.

These and other objects, advantages, and features will become readilyapparent in view of the following more detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an embodiment of the present invention.

FIG. 2 schematically illustrates the adjustable slit illustrated in FIG.1.

FIG. 2A schematically illustrates the partial coherence adjusterillustrated in FIG. 1.

FIG. 3A illustrates a reticle having a vertical feature.

FIG. 3B illustrates a reticle having a horizontal feature.

FIG. 4A illustrates a reticle having a feature oriented in a firstdirection.

FIG. 4B illustrates a reticle having a feature oriented in a seconddirection.

FIG. 5 is a cross section schematically illustrating lineslithographically produced on a substrate.

FIG. 6 schematically illustrates variable widths in a portion of alithographically produced line.

FIG. 7 is a plan view schematically illustrating an orthogonal linepattern.

FIG. 8 is a plan view schematically illustrating a printed line patternwith horizontal bias.

FIG. 9 is a plan view schematically illustrating a printed line patternwith vertical bias.

FIG. 10 is a plan view schematically illustrating a test reticle havingdifferent fields with different line widths.

FIG. 11 is a plan view schematically illustrating different locationsalong a slit.

FIG. 12 is a plan view schematically illustrating a reticle havingdifferent horizontal features at different spatial locations.

FIG. 13 is a plan view schematically illustrating a reticle havingdifferent vertical features at different spatial locations.

FIG. 14 is a graph illustrating the mask error factor.

FIG. 15 is a block diagram illustrating the method steps of anembodiment of the present invention for adjusting exposure dose.

FIG. 16 is a block diagram illustrating the method steps of anembodiment of the present invention for correcting horizontal bias byvarying partial coherence.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a photolithographic device of thepresent invention. A mask or reticle 10 having a pattern thereon isimaged onto a photosensitive substrate or wafer 12. The image of themask or reticle 10 is projected through projection optics 14 onto thesubstrate 12. An illumination source or system 16 is used to project theimage of mask or reticle 10 onto the photosensitive substrate 12. Apartial coherence adjuster or array optical element 18 selectivelyvaries the emerging numerical aperture of the illumination along theslot illumination field and in a scan direction and therefore adjuststhe partial coherence of the system. Adjustable slit 20 forms anillumination field, which is scanned over the reticle 10. A mask stage22 and a substrate stage 24 are controlled by the stage control 26 andmoved in synchronization so that the illumination field formed by theadjustable slit 20 scans the entire reticle 10 to reproduce an imagethereof on the photosensitive substrate 12. The mask or reticle stage 22and the substrate stage 24 move in the direction of arrow 17. Theadjustable slit 20 is controlled by an adjustable slit control 28. Theadjustable slit control 28 is coupled to an exposure calculator 30 and adata storage device 32. The partial coherence adjuster 18 is coupled toa partial coherence adjuster control 33. The partial coherence adjustercontrol 33 controls the movement of the partial coherence adjuster toprovide a predetermined adjustment to the partial coherence of thesystem. The partial coherence adjuster or optical element 18 may besimilar to the optical element disclosed in U.S. patent application Ser.No. 09/599,383 entitled “Illumination System With Spatially ControllablePartial Coherence Compensating For Linewidth Variance In APhotolithographic System” filed by McCullough et al on Jun. 22, 2000,which is herein incorporated by reference in its entirety. The partialcoherence adjuster 18 may also be a gradient array with selecteddifferent portions being used to control the partial coherence of theillumination at predetermined locations in the illumination field andduring scanning. The partial coherence adjuster may be moved oreffectively moved with optical elements to select the desired portionfor creating the partial coherence. A system control 35 is coupled tostage control 26, partial coherence adjuster control 33, adjustable slitcontrol 28, exposure calculator 30, and data storage 32.

The embodiment of the invention illustrated in FIG. 1 allows forcorrection of feature size variations resulting from a mask errorfactor. If the mask error factor varies as a function of reticle featuresize then the mask error factor causes deviation of the printed featureas a function of the feature size. The mask error factor may be definedby the following equation:

Mask Error Factor=Image Reduction Factor×Change in WaferLinewidth/Change in Reticle Linewidth.

If the mask error factor is one or a constant, which is desirable, thencalibration may be used to adjust linewidth.

The reticle linewidths are measured in the reticle plane and the waferlinewidths are measured in the wafer plane. The mask error factor causesthe linewidths to print with different image reduction factors fordifferent feature sizes and feature types. Linewidth variations at bestfocus over the usable depth of focus are influenced. The presentinvention reduces or eliminates the effect of the mask error factor byadjusting the exposure dose and partial coherence along the slot andscan directions. Linewidth control at best focus and through a givenfocus range for different orientations of a given feature type istherefore improved.

The mask error factor for a given feature type and orientation may bemodeled or calculated from either aerial image measurements orlithographical measurements at as many different locations along theslot as needed based upon the significance of its variation along theslot. The mask error factor can be measured for different conditions ofthe photolithographic device or tool, such as pupil fill, partialcoherence, numerical aperture, and for different operating conditionssuch as accumulated dose, number of fields per wafer, number of wafersper batch, among others. Once the features on the reticle, such aslines, contacts, are specified, the principal characteristics may bemeasured lithographically or by aerial image measurements. Modeling bysoftware computer simulations with industrial standard modeling or otherequivalent modeling techniques that are well known may be used.Generally, a feature size reduction from a reticle feature to aphotosensitive substrate feature has a fixed image reduction factor,such as 4 to 1. However, other reduction factors are possible and oftenused. However, as the feature size varies around a nominal size,reduction factor may change. Departure from the nominal image reductionfactor causes undesirable linewidth variations across the printedfields. As a result, feature size from the recticle is not consistentlyreproduced on the wafer with the nominal image reduction factor and isdifferent for different feature sizes around the nominal value. However,once the reticle feature size variations around the nominal value aremeasured, they can be corrected by modifying the exposure dose at eachpoint in the illumination field during the scanning exposure. This isaccomplished by the use of the adjustable slit 20.

Knowing the resist characteristics and linewith variation per unit dosechange, the dose changes required to correct for different mask errorfactor effects at different feature sizes across the field, bothlongitudinally along the slot and in the scan direction, can becalculated. These calculations are then used to modify the dose duringscanning to reduce or eliminate the effects of mask error factor on theprinted linewidth. The printed linewidth error on the substrate or wafermay be calculated by the following equation.

Change in printed wafer Linewidth=[Mask Error Factor×Change in ReticleLinewidth]/Nominal Image Reduction Factor.

If the mask error factor is constant; that is, it does not vary withreticle feature size variation around the nominal, then it can becorrected by dose calibration or magnification control. When the maskerror factor varies from one field location on the reticle to another,that is it changes as reticle feature size changes around the nominal,it cannot be corrected by the nominal dose calibration. The dose mustthen be varied as the reticle is scanned by the adjustable slit 20.Knowing the mask error factor and the reticle linewidth, reticlecorrection calculations can be made and applied during tool use fordevice manufacturing and characterization. If the mask error factor isthe same for different feature types, then a correction can be made withthe adjustable slit in a single exposure, assuming that differentorientations have similar feature dimensions. The dose correction iscalculated at each field location on the reticle. The reticle linewidthvariation correction calculation may be made as follows:

MEF=m[ΔCD_(wafer)/ΔCD_(reticle)]

MEF is the Mask Error Factor and is defined for mask linwidth at eachfield location. Typically MEF is equal to one.

m is the Nominal Image Reduction Factor or NIRF. Therefore,

 [ΔCD_(reticleH)×MEF_(H)]/m=ΔCD_(waferH)=Predicted Horizontal linewidthon wafer

[ΔCD_(reticleV)×MEF_(V)]/m=ΔCD_(waferV)=Predicted Vertical linewidth onwafer

For MEF_(H)≈MEF_(V)=MEF at any given location in the field.

ΔCD_(wafer)=(ΔCD_(waferH)+ΔCD_(waferV))/2=MEF[ΔCD_(reticleH)+ΔCD_(reticleV)]/2MAlternatively, if MEF_(H) is not equal to MEF_(V) then,

ΔCD_(wafer)=[(ΔCD_(reticleH)) MEF_(H)+(ΔCD_(reticleV)) MEF_(V)]/2M

ΔDose Correction=ΔCD_(wafer)/Dose sensitivity

The ΔDose Correction is calculated at each location in the exposurefield.

However, if there is a residual horizontal/vertical bias after theaverage linewidth is corrected as indicated above, that is (a) ahorizontal feature is imaged differently than a vertical feature at thesame location, or (b) a horizontal feature that is different than avertical feature size on the reticle, then the mask error factor may becontrolled with the partial coherence adjuster or array optical element18 by modifying the partial coherence at different spatial locations inboth a direction along the illumination slot and in the direction ofscan. Alternatively, multiple exposures may be utilized such thatfeatures with different orientations can be printed in separateexposures with the dose controlled by the adjustable slit 20 setindependently.

Linewidth variations can be corrected by calculating the horizontal andvertical feature size biases at each site on the reticle and by usingthe mask error factor control. Either by measurement or modeling, theprinted horizontal features and printed vertical features may becalculated in the wafer plane. The horizontal and vertical bias may alsobe calculated in the wafer plane. The partial coherence variancerequired for correcting the horizontal and vertical bias can becalculated by techniques well known in the art and with the aid ofcommercial software that is readily available. The optical element 18 isthen utilized to vary the partial coherence at each spatial location inthe slit field to compensate for the horizontal and vertical bias. Oncethe partial coherence at the spatial location is determined, the partialcoherence correction as provided by the partial coherence adjuster oroptical element 18 may be applied.

Accordingly, the present invention may be utilized to correct foraverage reticle linewidth variations or to correct for horizontal andvertical bias variations, or to correct for both average reticlelinewidth variations and horizontal and vertical bias variations, or tocorrect for horizontal linewidth variations only, or to correct forvertical linewidth variations only.

FIG. 2 schematically illustrates the adjustable slit 20 illustrated inFIG. 1. An illumination field 40 is created by an illumination adjuster38 that creates an adjustable contour 36. The adjustable contour 36 inillumination adjuster 38 blocks portions of the substantiallyrectangular illumination field to adjust the width of the illuminationfield at different longitudinal positions. Therefore, the illuminationfield 40 will have a maximum width W_(max) or a minimum width W_(min).An adjustable contour drive 34 adjusts the adjustable contour 36. Theadjustable contour drive 34 is controlled by the adjustable slit control28.

In operation, the adjustable slit 20 modifies the exposure dose receivedby the photosensitive substrate 12, illustrated in FIG. 1. Thesubstantially rectangular illumination field 40 is scanned in thedirection of arrow 42 to project the image of the reticle 10 onto aphotosensitive substrate. The reticle 10 is held in a reticle stage 22and driven by a stage control 26 so as to scan the illumination field40. As the illumination field 40 is scanned across the reticle 10, theadjustable slit control 28 controls the adjustable contour drive 34,causing the illumination adjuster 38 to vary the adjustable contour 36.The exposure calculator 30 is coupled to the adjustable slit control andis used to determine the correct exposure dose. Data storage 32 storesdata relating to exposure dose required to obtain the desired change inlinewidth.

FIG. 2A schematically illustrates the optical array element or partialcoherence adjuster 18 illustrated in FIG. 1. The partial coherenceadjuster or array optical element 18 is used to vary the emergingnumerical aperture of the illumination source used to form theillumination field. This in turn varies the partial coherence, which isdefined as the ratio formed by the numerical aperture of the illuminatoroptical system divided by the numerical aperture of the projectionoptical system. The partial coherence adjuster 18 is formed from aplurality of regions 19. Each region 19 may be made of a lens orplurality of lenses that modify the emerging numerical aperture or coneof illumination in a predetermined way. The different regions 19 mayalso be continuous or a gradient rather than discrete. The partialcoherence adjuster or array optical element 18 is dynamic in the sensethat it can select a portion of the reticle to provide a predeterminedpartial coherence. Therefore, a partial coherence change may be made atany pre-selected point in the illumination field depending upon theadjustment to be made to the printed image.

The partial coherence adjuster 18 may be fixed and the desired regions19 optically selected by a region selector 18A. That is other opticalelements may be positioned adjacent the desired region 19 to provideillumination for forming the desired partial coherence. The regionselector 18A may be comprised of movable mirrors, prisms, fiber opticelements, adjustable slots or slits, or other well known opticalelements or devises.

FIGS. 3A and 3B schematically illustrate reticles having differentfeature types. Reticle 110A has a vertical feature type 111A, andreticle 110B has a horizontal feature type 111B.

FIGS. 4A and 4B illustrate reticles having other different featuretypes. In FIG. 4A, a reticle 110C has a first feature type 111C thereon.In FIG. 4B, a reticle 110D has a second feature type 111D thereon. Thefirst and second feature types 111C and 111D may be orientated atdifferent angles relative to the reticle orientation. It should beappreciated that there are a large number of feature types that arefound on different reticles. The feature types illustrated in FIGS. 3A-Band FIGS. 4A-B are illustrative of the different orientations ofdifferent feature types. Many feature types are primarily horizontal andvertical or orthogonal with respect to each other. Feature types mayalso include isolated and/or grouped features. Other examples includelines, contacts, and other well known features used in photolithographyfor the manufacture of semiconductor devices.

FIG. 5 schematically illustrates a cross section of a portion of asemiconductor device manufactured with a lithographic technique. Placedon substrate 112 is a first line 112A and a second line 112B. While onlyone layer is illustrated, typically many different layers are utilizeddepending upon the semiconductor device being manufactured. The firstline 112A has a lateral width W and a space between adjacent lines 112Aand 112B. However, the term linewidth may also be used to indicate thespace between adjacent lines 112A and 112B.

FIG. 6 is a plan view of vertical lines 115A, 115B, 115C and horizontallines 113A, 113B, 113C, similar to the lines illustrated in FIG. 5. Thelines 115A-C and 113A-C are printed at various locations along the slotprojected on the photosensitive substrate. The lines 115A-C and 113A-Care generally orthogonal to each other, but may have differentorientations. Additionally, the linewidth should accurately reflect thelinewidth of the reticle, which is imaged on the photosensitivesubstrate. However, with very small linewidths, of the order of theexposure wavelength or smaller, it is often very difficult to obtain thesame linewidth across the slot as well as a linewidth that does notdeviate from the linewidth on the reticle due to differentphotolithographic parameters or variables. Accordingly, the linewidthsmay have different widths W′_(V), W″_(V), W′″_(V), W′_(H), W″_(H) andW′″_(H) at different longitudinal locations along the slot projectedonto the photosensitive substrate. The present invention, by controllingthe dose with the adjustable slit 20, illustrated in FIGS. 1 and 2,reduces the variation in linewidth, especially as a function of featuresize and location.

Additionally, there may be errors or variations of linewidth as a resultof the manufacturing of the reticle. The present invention byselectively controlling the exposure dose and partial coherence atdifferent locations in the exposure field along the slot can correct formanufacturing errors of the reticle. Therefore, a designed or intendedlinewidth can be printed even though an error in the linewidth on thereticle has occurred during manufacture of the reticle. This feature ofthe present invention can also reduce the required manufacturingtolerances of reticles, and therefore substantially reduce themanufacturing cost of producing reticles. For example, a reticle havingreduced manufacturing tolerances may be made at reduced cost or areticle that has some dimensional errors at different locations maystill be used. The deviation from the proportioned dimensions of thereticle image to be reproduced may be compensated for by the presentinvention resulting in the reproduction of the desired image. Byproportioned dimensions it is meant that the image of the reticle may bereduced by a reduction factor or magnification of less than one, forexample a four to one reduction ratio. Therefore, even though thereticle has reduced manufacturing tolerances the desired image can stillbe reproduced.

FIGS. 7-9 illustrate the effect of horizontal and vertical bias inprinting orthogonal linewidths. It should be appreciated that horizontaland vertical bias represents variations in linewidths between twohorizontal and vertical orientations. Biases in other orientations arealso applicable. FIG. 7 illustrates a horizontal line 212H having awidth of W_(H) and a vertical line 212V having a width of W_(V). WidthW_(H) is substantially equal to width W_(V). FIG. 8 illustrates printingof the line pattern illustrated in FIG. 7 with a photolithographicsystem having a horizontal bias at a particular location in the field.Due to the horizontal bias, horizontal line 212H′ has a changed printedlinewidth W_(H)′, while the vertical line 212V has substantially thesame linewidth W_(V) as illustrated in the line pattern in FIG. 7.Similarly, FIG. 9 illustrates printing of the line pattern illustratedin FIG. 7 with a photolithographic system having vertical bias at aparticular location in the field. Due to the vertical bias, verticalline 212V′ has a changed printed linewidth W_(V)′, while the horizontalline 212H has substantially the same linewidth W_(H) as illustrated inthe line pattern in FIG. 7. A photolithographic system may have apositive, wider linewidth, or a negative, narrower linewidth, bias or acombination of both horizontal and vertical bias at a single location.This horizontal and vertical bias will vary spatially within the fieldof the photolithographic system and may be different for each system.

This horizontal and vertical bias, along with other imagingcharacteristics of the photolithographic system, is often referred to asthe signature of the photolithographic system. The signature of thephotolithographic system may also include characteristic of the reticlebeing used for imaging. In compensating for horizontal/vertical biasintroduced by the reticle and from mask error factor characteristics,the present invention utilizes the array optical element 18, illustratedin FIGS. 1 and 2A, to modify the partial coherence or fill geometry ofthe illumination to compensate for the horizontal and vertical bias atdifferent locations where required to accurately print an image of thereticle.

FIG. 10 schematically illustrates a test reticle 310 having a pluralityof m columns and n rows of a line pattern portion 311. The line patternportion 311 has a plurality of different linewidth spacings andorientations. Each of the line pattern portions 310 is positioned in anarray configuration on test reticle 310. The test reticle 310 isutilized to obtain the actual printed measurements to determinephotolithographic system or tool mask error factor at differentlocations along the slot for given feature types and sizes around thenominal sizes.

FIG. 11 illustrates the use of a slot or slit field 310 havingcorresponding line pattern portions 311 along the longitudinal lengthsof the slit field 320. The line pattern portions or group features maybe comprised of (a) varying linewidths for a constant pitch or (b)varying linewidths (i.e. varying pitch) having a 1:1 line/spacing dutycycle. The slot or slit field is scanned across the reticle 310,illustrated in FIG. 10. The actual tool mask error factor is thendetermined at various longitudinal locations along the slit field 320.This information is utilized to determine the appropriate exposure doseto be provided by the adjustable slit and the partial coherence to beprovided by the array optical element in correcting for linewidthvariation or any horizontal/vertical bias.

Utilizing this format or method data is available at multiple locationsalong the scan for a given slot position. This allows evaluation andcorrection for scan signature and also for a given feature type andsize.

FIG. 12 graphically or schematically illustrates different horizontalfeature sizes located at different spatial lactations on a reticle 410H.

FIG. 13 graphically or schematically illustrates different verticalfeature sizes located at different spatial lactations on a reticle 410V.

The different horizontal and vertical feature sizes are often combinedin the features of a single reticle. FIGS. 12 and 13 are intended toillustrate the different features have horizontal and verticalcomponents.

FIG. 14 is a graph illustrating the mask error factor. Dashed line 50represents a slope of one indicating that the reticle critical dimensionis the same as the wafer critical dimension and therefore there is nomask error factor related correction required during an exposure. Line52 represents a mask error factor for relatively small features when thefeature reproduced on the substrate or wafer is oversized relative tothe feature being reproduced from the reticle. Line 54 represents themask error factor for relatively small features when the featurereproduced on the substrate or wafer is undersized relative to thefeature being reproduced from the reticle. It should be noted that themask error factor increases substantially as the feature size becomessmaller. Accordingly, the present invention, in correcting for maskerror factor and the related imaging problems, becomes much moreimportant as the feature size becomes smaller for a given technologynode.

FIG. 15 is a block diagram illustrating the method steps of an elementof the present invention. FIG. 15 illustrates the method steps utilizedin correcting for the exposure dose to reduce linewidth variation. Box510 represents the step of measuring reticle linewidth variation fromthe nominal feature size and type. Box 512 represents the step ofcalculating the predicted wafer or printed linewidth variation at eachspatial location for different orientations. This calculation can beaccomplished utilizing the following equations:

[ΔCD_(reticleH)×MEF_(H)]/m=ΔCD_(waferH)=Predicted horizontal linewidthat wafer

 [ΔCD_(reticleV)×MEF_(V)]/m=ΔCD_(waferV)=Predicted Vertical linewidth onwafer

Box 514 represents the step of predicting the average printed waferlinewidth. This can be performed by the following equation:

ΔCD_(wafer)=(ΔCD_(waferH)+ΔCD_(waferV))/2

Wherein, ΔCD_(wafer) is the average of the horizontal and verticallinewidths.

Box 516 represents the step of calculating the dose correction at eachspatial location. This can be accomplished by the following equation:

ΔDose Correction=CD_(wafer)/Dose sensitivity

The dose correction is for a given feature, resist and type.

Box 518 represents the method step of a adjusting the dose with theadjustable slit at each spatial location. This step then compensates orcorrects the exposure dose to obtain a reduced variation of linewidthbased on the calculations from the prior method steps.

FIG. 16 is a block diagram illustrating an element of the presentinvention. FIG. 16 represents the method steps or acts utilized inmodifying the partial coherence of illumination to compensate forhorizontal and vertical bias. Box 610 represents the method step or actof calculating the horizontal/vertical bias at each spatial location onthe reticle. Box 612 represents the step or act of predicting theprinted horizontal/vertical bias using the mask error factor. Thehorizontal and vertical bias may be measured or obtained based oncalculations or modeling. Box 614 represents the method step ofcalculating the partial coherence variation required to correct for thehorizontal and vertical bias. This can be done by using variouscalculation methods or commercially available software, such as Prolithsoftware. Box 616 represents the method step of varying the partialcoherence at each spatial location based on the calculation of therequired partial coherence change or variation in order to obtain therequired correction for horizontal/vertical bias. Modifying or changingthe array optical element associated with the illumination source canaccomplish this. The array optical element may also be dynamic ormovable in a plane, as illustrated in FIG. 2A.

By combining the methods illustrated in FIGS. 15 and 16, improvedprinting can be obtained. Accordingly, by correcting both the dose atdifferent spatial locations and the partial coherence at differentspatial locations, variations in linewidth can be compensated for, aswell as horizontal and vertical bias. Therefore, the present inventionprovides an apparatus and method that is utilized with photolithographicdevices used in the manufacture of semiconductors to improve quality andyield. The present invention permits the imaging and printing of muchsmaller features or elements that may not be possible or easily obtainedusing current techniques. Therefore, the present invention advances thephotolithographic arts and the manufacture of semiconductors associatedtherewith.

The term horizontal and vertical bias is used to mean a change inprinted linewidth as a result of differences in orientation. While thelinewidths are typically perpendicular to one another, horizontal orvertical, the linewidths may have any relative orientation. Therefore,the term horizontal and vertical bias may be used interchangeably withorientation bias.

Although the preferred embodiments have been illustrated and described,it will be apparent to those skilled in the art that variousmodifications may be made without departing from the spirit and scope ofthis invention.

What is claimed is:
 1. A photolithographic device comprising: anillumination source; a partial coherence adjuster receivingelectromagnetic radiation from said illumination source; an adjustableslit receiving electromagnetic radiation from said illumination source;a reticle stage adapted to hold a reticle thereon; a substrate stageadapted to hold a photosensitive substrate thereon; and projectionoptics positioned between said reticle stage and said substrate stage,said projection optics projecting an image of the reticle onto thephotosensitive substrate, whereby the dose of electromagnetic radiationreceived by the substrate is changed by said adjustable slit and thepartial coherence of the illumination is modified at selected portionsof the reticle by the partial coherence adjuster resulting in linewidthvariation being controlled.
 2. A photolithographic device as in claim 1wherein: said partial coherence adjuster comprises an array opticalelement.
 3. A photolithographic device as in claim 2 further comprising:a region selector associated with said array optical element, whereby apartial coherence change may be made at any predetermined spatiallocation.
 4. A photolithographic device as in claim 2 wherein: saidarray optical element has a plurality of emerging numerical aperturemodifying regions.
 5. A scanning photolithographic device used inprinting an image of a reticle onto a photosensitive substratecomprising: an illumination source; an array optical element having aplurality of emerging numerical aperture modifying regions positioned toreceive electromagnetic radiation from said illumination source; anadjustable slit receiving electromagnetic radiation emerging from saidarray optical element; a reticle stage adapted to hold the reticlethereon; a substrate stage adapted to hold the photosensitive substratethereon; projection optics positioned between said reticle stage andsaid substrate stage, said projection optics projecting an image of thereticle onto the photosensitive substrate; a stage control, said stagecontrol coupled to said reticle stage and said substrate stage; and anadjustable slit control coupled to said adjustable slit, whereby thedose of electromagnetic radiation received by the photosensitivesubstrate is changed by said adjustable slit and said array opticalelement modifies the emerging numerical aperture at selected portions ofthe reticle resulting in linewidth variation being controlled.
 6. Ascanning photolithographic device used in printing an image of a reticleonto a photosensitive substrate as in claim 5 further comprising: aregion selector associated with said array optical element for changingthe emerging numerical aperture and resulting partial coherence atpredetermined spatial locations.
 7. A scanning photolithographic deviceused in printing an image of a reticle onto a photosensitive substrateas in claim 5 wherein: said adjustable slit has a variable width along alongitudinal length.
 8. A scanning photolithographic device used inprinting an image of a reticle onto a photosensitive substrate as inclaim 5 further comprising: a test reticle having a plurality of linepattern portions with lines of different linewidths and orientationsspatially positioned, whereby locations of the linewidth variations onthe photosensitive substrate can be determined.
 9. A scanningphotolithographic device used in printing an image of a reticle onto aphotosensitive substrate as in claim 5 further comprising: means,associated with the photosensitive substrate, for determining thevariations of linewidth on the photosensitive substrate when processed.10. A scanning photolithographic device used in printing an image of areticle onto a photosensitive substrate comprising: an illuminationsource providing an illumination field; means, positioned to receiveelectromagnetic radiation from said illumination source, for varyingpartial coherence at selected portions of the illumination field; meansfor determining variations in linewidth in a printed field relative tothe reticle at a plurality of locations; means, coupled to said meansfor determining variations in linewidth, for calculating a partialcoherence correction at each of the plurality of locations to reduce thevariations in linewidth in the printed field; means, coupled to saidmeans for varying partial coherence, for adjusting a partial coherenceat each of the plurality of locations based upon the partial coherencecorrection; means, positioned to receive electromagnetic radiation fromsaid illumination source, for varying an exposure dose at differentspatial locations on the photosensitive substrate; means for determiningvariations in linewidth in a printed field relative to the reticle at aplurality of linewidth variation locations; means, coupled to said meansfor determining variations in linewidth, for calculating an exposuredose correction at each of the plurality of linewidth variationlocations to reduce the variations in linewidth in the printed field;means, coupled to said means for varying an exposure dose, for adjustingan exposure dose at each of the plurality of linewidth variationlocations based upon the exposure dose correction; a reticle stageadapted to hold the reticle thereon; a substrate stage adapted to holdthe photosensitive substrate thereon; projection optics positionedbetween said reticle stage and said substrate stage, said projectionoptics projecting an image of the reticle onto the photosensitivesubstrate; and means, coupled to said reticle stage and said substratestage, for synchronously scanning said reticle state and said substratestage, whereby the electromagnetic radiation received by the substrateis changed resulting in the variations in linewidth on the printedsubstrate being controlled.
 11. A scanning photolithographic device usedin printing an image of a reticle onto a photosensitive substratecomprising: an illumination source; an array optical element having aplurality of emerging numerical aperture modifying regions andcomprising a gradient, positioned to receive electromagnetic radiationfrom said illumination source and provide a selected partial coherenceat predetermined locations on the reticle; a region selector associatedwith said array optical element, said region selector redirecting theplurality of emerging numerical aperture modifying regions atpredetermined locations; an adjustable slit having a longitudinaldimension positioned to receive electromagnetic radiation from saidillumination source, said adjustable slit having a variable width alongthe longitudinal dimension; a reticle stage adapted to hold the reticlethereon; a substrate stage adapted to hold the photosensitive substratethereon; projection optics positioned between said reticle stage andsaid substrate stage, said projection optics projecting an image of thereticle onto the photosensitive substrate; a stage control, said stagecontrol coupled to said reticle stage and said substrate stage; anadjustable slit control coupled to said adjustable slit; and a systemcontrol coupled to said stage control, said region selector, and saidadjustable slit control, whereby the dose of electromagnetic radiationreceived by the photosensitive substrate is changed by said adjustableslit and said array optical element modifies the selected partialcoherence at predetermined spatial locations on the reticle resulting inlinewidth variation being controlled.
 12. A scanning photolithographicdevice used in printing an image of a reticle onto a photosensitivesubstrate as in claim 11 further comprising: means, coupled to saidsystem control, for calculating a corrected exposure dose and emergingnumerical aperture to reduce the variations in linewidth on thephotosensitive substrate.
 13. A method of exposing a photosensitivesubstrate with an image of a reticle comprising the steps of: varying anexposure dose of electromagnetic radiation at different linewidthvarying spatial locations on the photosensitive substrate; and varying apartial coherence of the electromagnetic radiation used to image thereticle on the photosensitive substrate at different spatial locationson the photosensitive substrate by varying the partial coherence atselected portions of the reticle, whereby linewidth variance in theprinted image of the reticle are reduced.
 14. A method of exposing aphotosensitive substrate as in claim 13 further comprising the steps of:calculating an exposure dose correction at each of the differentlinewidth varying spatial locations on the photosensitive substrate; andcalculating a partial coherence correction at each of the differentspatial locations on the photosensitive substrate.
 15. A method ofexposing a photosensitive substrate to vary linewidth on a printedsubstrate comprising the steps of: determining variations in linewidthrelative to a reticle at a plurality of locations in a printed field;calculating an exposure dose correction at each of the plurality oflocations to reduce the variations in linewidth in the printed field;adjusting the exposure dose of the electromagnetic radiation used toexpose the photosensitive substrate at each of the locations based uponthe exposure dose correction; determining variations in linewidthrelative to the reticle at the plurality of locations; calculating apartial coherence correction at each of the plurality of locations toreduce the variations in linewidth in the printed field; and adjustingthe partial coherence of the electromagnetic radiation used to exposethe photosensitive substrate at each of the plurality of locations basedupon the partial coherence correction, whereby linewidth variations inthe printed field are reduced.
 16. A method of exposing a photosensitivesubstrate to control linewidth on a printed substrate comprising thesteps of: determining variations in linewidth on the printed substratedeviating from an intended linewidth at a plurality of locations in aprinted field; calculating an exposure dose correction at each of theplurality of locations to control the intended linewidth in the printedfield; adjusting the exposure dose of the electromagnetic radiation usedto expose the printed substrate at each of the different linewidthlocations based upon the exposure dose correction; determiningvariations in linewidth relative to the intended linewidth at theplurality of locations in the printed field; calculating a partialcoherence correction at each of the plurality of locations to controlthe variations in linewidth in the printed field; and adjusting thepartial coherence of the electromagnetic radiation used to expose theprinted substrate at each of the plurality of locations based upon thepartial coherence correction, whereby the linewidth in the printed fieldis controlled to obtain the intended linewidth on the printed substrate.17. An exposure control device used in a photolithographic apparatuscomprising: an adjustable slit positioned to receive the electromagneticradiation from an illumination source; and a partial coherence adjusterpositioned to receive electromagnetic radiation form the illuminationsource, whereby an exposure dose and partial coherence of theelectromagnetic radiation is selectively varied at predeterminedportions of a photosensitive substrate for reducing variations inlinewidth.
 18. An exposure control device as in claim 17 wherein: saidpartial coherence adjuster comprises a plurality of different emergingnumerical aperture regions, whereby partial coherence is modified. 19.An exposure control device as in claim 18 further comprising: a regionselector associated with said partial coherence adjuster, whereby aselected one of the plurality of different emerging numerical apertureregions is selected.
 20. A method of printing an image of a reticlehaving dimensions deviating from proportioned desired dimensions onto aphotosensitive substrate comprising the steps of: manufacturing areticle having dimensions that deviate from proportioned desireddimensions to be printed on the photosensitive substrate; adjusting adose of illumination at different spatial locations to vary printedfeature linewidths so as to obtain the proportioned desired dimensionsto be printed on the photosensitive substrate; adjusting a partialcoherence of illumination at selected portions of the reticle to varyprinted feature linewidths so as to obtain the proportioned desireddimensions to be printed on the photosensitive substrate, whereby thereticle may be utilized even though it has relaxed manufacturingtolerances.
 21. A photolithographic method of printing an image of areticle having dimensions deviating from proportioned desired dimensionsonto a photosensitive substrate comprising the steps of: manufacturing areticle having dimensions that deviate from proportioned desireddimensions to be printed on the photosensitive substrate; calculatingadjustments to a dose of illumination at different spatial locationsneeded to vary printed feature linewidths so as to obtain theproportioned desired dimensions to be printed on the photosensitivesubstrate; adjusting the dose of illumination based upon the step ofcalculating the dose of illumination at the different spatial locationsto vary printed feature linewidths so as to obtain the proportioneddesired dimensions to be printed on the photosensitive substrate;calculating adjustments to a partial coherence of illumination atselected portions of the reticle to vary the printed feature linewidthsso as to obtain the proportioned desired dimensions to be printed on thephotosensitive substrate; adjusting the partial coherence ofillumination based upon the step of calculating adjustments to thepartial coherence at different spatial locations to vary the printedfeature linewidths so as to obtain the proportioned desired dimensionsto be printed on the photosensitive substrate, whereby the reticle maybe utilized even though it has relaxed manufacturing tolerances.